Respirator masks are used in a wide variety of environments, such as, e.g., paint booths, grain storage facilities, laboratories with hazardous biological materials, environments containing certain chemical fumes, etc. Respirator masks are typically adapted to receive a variety of filter units and other attachments that are designed specifically for the hazardous environment in which the mask is to be used. As such, the same mask body can be used in a variety of different hazardous environments simply by changing the filter. This ease of changing filters makes the masks very cost effective by permitting the manufacture of a single mask for multiple environments.
Respirator masks define a clean air envelope with the face of the wearer. The clean air envelope includes the clean air source and is bounded by the mask, the mask's seal with the face of the wearer, and the exhalation valve of the mask.
There are two general designs of respirator face masks: the partial facepiece respirator mask and the full facepiece respirator mask. A partial facepiece respirator mask typically encloses the wearer's mouth and nose and forms a seal with the portion of the wearer's face that is contiguous to the nose and mouth. The eyes are left unprotected when using the partial facepiece respirator mask. The full facepiece respirator mask is a much larger unit and encloses the wearer's eyes in addition to the wearer's nose and mouth.
Respirator masks can additionally be distinguished by being either a positive pressure or negative pressure device. A positive pressure device typically includes an external pump or pressurized vessel, with or without a filter, that is the clean air source and that forces air into the mask. A negative pressure respirator mask functions on the negative pressure generated by the wearer inhaling. The inhalation generates a negative pressure inside the clean air envelope and draws air into the respirator mask. Generally, ambient air is drawn through a filter or filters by the negative pressure. The filters clean the air and the air is then drawn into the clean air envelope of the mask for inhalation by the wearer.
Attempts have been made to enhance the intelligibility of speech in connection with respirator masks because the masks cover the wearer's mouth. Passive devices are purely mechanical and active devices involve some form of enhancement by powered amplification. The most common passive communication device is the voice diaphragm. Although voice diaphragms are useful, the level of enhanced intelligibility they provide is limited.
Active speech transmission devices can provide better enhancement of speech, but may be limited by the power required to operate the units. Examples of some active speech amplification units are described in U.S. Pat. Nos. 4,352,353; 4,508,936; 4,989,596; 4,980,926; 5,138,666; 5,224,473; 5,224,474; 6,382,206; etc.